Potentiation of interleukin-2 activity by levamisole and imidazole.

Levamisole, a known antihelminthic drug, was able to affect IL-2 dependent proliferation of several T lymphocyte clones. Although levamisole did not replace IL-2 and had no effect at saturating IL-2 concentrations, it reduced by 2- to 4-fold the dose of IL-2 required to give 50% of the maximal DNA synthesis, the optimal concentration of levamisole being between 1 to 3 X 10(-4) M. This effect of levamisole was not due to an alteration of the kinetics of thymidine incorporation. Imidazole and other imidazole ring containing compounds, but not thiol-containing compounds, had similar effects to those of levamisole, suggesting a role of the imidazole ring in the potentiation of IL-2 activity.